Problem: $(80i)-(80+10i)=$ Express your answer in the form $(a+bi)$.
Solution: Background Complex numbers can be added or subtracted by separately adding or subtracting their real and imaginary terms. To add or subtract complex numbers: Expand parentheses (attending to minus signs outside of parentheses if necessary) Combine all real terms (terms that do not contain $i$ ), and add or subtract them. Combine all imaginary terms (terms that contain $i$ ), and add or subtract them. Combining Like Terms $\begin{aligned} ({80}i)-({80}+{10}i)&={80}i-{80}-{10}i \\\\ &={-80}+{80}i-{10}i \\\\ &={-80}+{70}i \end{aligned}$ Summary $({80}i)-({80}+{10}i)={-80}+{70}i$